440 
Marine Cercariae 
in spherical thiu-walled cysts 044 mm. across or smaller. The young 
cercariae are tailed (tail not quite so long as the body) and very active 
inside the sporocysts. The tails disappear some time before encystment. 
The cercaria when pressed out of the cyst measures 049 mm. in 
length. The body is covered with spines arranged in transverse rows. 
Oral sucker 0’04 mm. across, short prepharynx, conspicuous pharynx, 
short oesophagus, lobes of intestine reaching nearly to the posterior end 
of the body. Small ventral sucker slightly behind the centre of the 
body. Large bilobed excretory vesicle. 
The specimens were obtained in March, April and October. Tailed 
forms were only obtained in October. Those found in the spring con¬ 
tained the encysted cercariae in the spm’ocysts which possibly had 
been resting through the winter. 
The final host of Lepodora rachiaea is the haddock which feeds 
much on cockles. This cercai’ia is very like L. rachiaea and is in all 
probability that species which passes directly into its final host by the 
haddock eating the cockle. 
2. Cercariae developed in Rediae. 
(a) Cercaria neptimeae sp. inq. 
(PI. XXVIII, figs. 1, 2.) 
This is most difficult to place as in some respects it resembles the 
stumpy-tailed cercariae, in others it is like Acanthopsolus, and in the 
possession of a huge tail it is unlike either. 
It occurs in the digestive gland of Neptunea antiqua brought in by 
the Cullercoats fishing boats, and also from Buccinum undatum from 
the same locality in July. In both the reproductive organs are de¬ 
stroyed. The whole spire is packed with the rediae which are colourless 
and measure about 2 mm. or more in length. The i;edia has a pharynx 
0'04 mm. long, and a very short intestine, hardly longer than the 
pharynx. It contains the cercariae in various stages. 
The cercaria measures 04 mm. in length without its tail, breadth 
in extended condition about 040 mm., but very variable. The body is 
covered with small spines. Tail exceedingly large and thick forming 
an effectual swimming organ, length about 0'26 mm., breadth when 
moderately extended about 0'049 mm. Oral sucker 0'033 mm. across 
when circular but it can be elongated considerably so as to be longer 
than broad. Prepharynx O'Ofi mm. long, pharynx 0'03 mm. long, rest 
of alimentary canal not visible. Two large eye-spots just in front and 
